Within the field of astronomical observations, in order to observe celestial bodies of which the equatorial coordinates (Right Ascension and Declination) are known, the telescope polar axis requires to be aligned with the Earth polar axis. Thereby, the effect of the Earth's rotation can be cancelled about the polar axis, by means of an antagonist Right Ascension movement. Accordingly, a number of systems are known to achieve this polar position, both with motor-driven mounts and manually operated mounts.
These known systems, however, are not free of drawbacks, which are even more accentuate both in portable telescopes and telescopes that can be disassembled.
A drawback with many known systems is that, at the position time, they depend on the visibility of reference stars near the Celestial Pole (such as the North star in the Northern Hemisphere).
Another drawback of many known systems is that they are based on a reticle overlapped to the image provided by the polar eyepiece. This reticle allows to, after the parameters of date, time and place of observation have been set, properly orientate the telescope by simply matching several points that are marked on the reticle with the respective reference stars.
Since parameters depending on date, time and place of observation should be taken into account, a great level of skill and experience is required of the operator.
Furthermore, this system, which is potentially perfect on the telescope manufacturing date, introduces a small error which will however increase with the passing of years. The equinox precession, in fact, causes the reference stars to progressively move away from the positions marked on the eyepiece reticle. This movement, even though slow, introduces errors that can be appreciated 4-5 years after the telescope manufacture date.
A further drawback common to all known systems is that they strongly depend on the operator's skill, where by “skill” is meant his/her astronomic knowledge, operative ability and experience.
A further drawback depends on the fact that often the telescopes are not perfectly collimated and thus the proper position of the polar telescope does not determine the correct position of the main telescope as it is supposed to do.
A further drawback, typical of the so-called “Bigourdan's method” and the like, is that the position is carried out by successive approximations which are intended to gradually reduce the error. With these systems, obviously, the operator is required to reach a compromise between either speed or precision of the positioning procedure. Very demanding operators can even take several hours to achieve a satisfactory position, while a position of several tens of minutes will necessarily result to be inaccurate.